The Coefficient of Thermal Expansion (CTE) of a polymer material—specifically, an epoxy resin—is about 50 to 80 ppm/° C., a significantly higher several to ten times than the CTE of a inorganic material such as ceramic material or a metal (for example, the CTE of silicon is 3 to 5 ppm/° C. and the CTE of copper is 17 ppm/° C.). Thus, when the polymer material is used in conjunction with an inorganic material or metal in a semiconductor, a display, or the like, the properties and processability of the polymer material may be significantly limited due to the mismatch in the coefficients of thermal expansion of the polymer material and the inorganic material or the metal material. In addition, during semiconductor packaging in which a silicon wafer and a polymer substrate are used side by side, or during a coating in which a polymer film is coated with an inorganic shielding layer to impart gas barrier property, product defects such as the generation of cracks in an inorganic layer, the warpage of a substrate, the peeling-off of a coating layer, the failure of a substrate, and the like, may be generated due to a large mismatch of coefficient of thermal expansion (CTE-mismatch) between constituent elements upon the changes in processing and/or applied temperature conditions.
Because of the high CTE of the polymer material and the resultant dimensional change of the polymer material, the development of technologies such as next generation semiconductor substrates, printed circuit boards (PCBs), packaging, organic thin film transistors (OTFTs), and flexible display substrates may be limited. Particularly, currently, in the semiconductor and PCB fields, designers are facing challenges in the design of next generation parts requiring high degrees of integration, miniaturization, flexibility, performance, and the like, in securing processability and reliability in parts due to polymer materials having significantly high CTE as compared to metal/ceramic materials. In other words, due to the high thermal expansion property of the polymer material at processing temperatures, defects may be generated, processability may be limited, and the design of the parts and the securing of processability and reliability therein may be objects of concern. Accordingly, improved thermal expansion property or dimensional stability of the polymer material is necessary in order to secure processability and reliability in electronic parts.
In general, in order to improve thermal expansion property—i.e., to obtain a low CTE value in a polymer material such as an epoxy resin, (1) a method of making a composite of the epoxy resin with inorganic particles (an inorganic filler) and/or fabrics and (2) a method of designing and synthesizing a novel epoxy resin with a decreased CTE have been used.
When the composite of the epoxy compound with the inorganic particles as the filler is formed in order to improve thermal expansion property, a large amount of inorganic silica particles, having a diameter of about 2 to 30 μm are required to be used to obtain the significant decrease of CTE. However, due to the addition of the large amount of inorganic particles, the processability and performance of the parts may be deteriorated. That is, the presence of the large amount of inorganic particles may decrease fluidity, and voids may be generated during the filling of narrow spaces. In addition, the viscosity of the material may increase exponentially due to the addition of the inorganic particles. Further, the size of the inorganic particles tends to decrease due to the miniaturization of semiconductor structure. When a filler having a particle size of 1 μm or less is used, the decrease in fluidity (increase in viscosity) may be worsened. When inorganic particles having a large average particle diameter are used, the frequency of insufficient filling in the case of a composition including a resin and the inorganic particles may increase. While the CTE of the composite may be decreased significantly when a composition including an organic resin and a fiber as the filler is used, it may remain still high as compared to that of a silicon chip or the like.
As described above, the manufacturing of highly integrated and high performance electronic parts for next generation semiconductor substrates, PCBs, and the like, may be limited due the limitations in the composite technology of epoxy compounds. Thus, the development of a epoxy composite having improved heat resistance property—namely, a low CTE and a high glass transition temperature—and good crosslinking density is required to overcome the a lack of heat resistance property due to a high CTE and poor processability of a common thermosetting polymer composite.